Linus isn't a dick though; indeed, he's quite laid-back and personable. When he criticizes someone like this, his criticisms are almost universally very accurate, and he only uses "extreme" language when (1) the person he's addressing did something really stupid ("merely stupid" isn't enough) and (2) that person really should have known better (so he doesn't tend to do this to strangers, only people he's well acquainted with, and has some trust in). He doesn't just call people names, he makes detailed technical arguments which happen to be decorated with er, expressive language.
This particular style is very common in the tech world, and if anything, Linus is far better than most, because he strictly sticks to technical criticisms; his language may be extreme, but for him, it isn't personal—if he is wrong, he'll very quickly admit it and apologize. Almost all of the time, the conversation quickly calms down and settles into a discussion of how to make things right. Note that this makes him vastly better than average: there are many others in the tech community who do take things personally, and won't back down no matter how obviously wrong they are.
This style isn't to everyone's tastes, and to someone who isn't familiar with Linus or the LKML, I guess it can be startling to see one of these exchanges. Maybe there are times when he goes too far. But claims that he's "abusive" are simply laughable. Things are not always as they appear at first glance...